1. Most obviously, the position of the switch on the rear of the card is used immediately after a system reset to force the selection of one of two banks of ROMs: the firmware card or the motherboard. If the switch is up then the system will default to Applesoft, otherwise the system will default to Integer BASIC.
2. Software, by accessing address $C080, can select Integer BASIC, or, by accessing address $C081, Applesoft.
Unfortunately for systems with Auto Start ROM, every time DOS gets control immediately after a reset, DOS forces a load of the version of BASIC DOS last used, regardless of the position of the switch.